The invention relates to processes for the combinatorial production of a library of materials in the surface region of a planar substrate by sputtering.
The parallelized production and testing of materials having suitable physical and/or chemical properties is a sector in material research which is currently greatly increasing in importance.
WO 98/47613 discloses a number of processes by which, using sputtering, CVD or PVD techniques, libraries of materials of potential interest can be generated. Basically, this application relates to the use of suitable masking techniques which makes possible defined deposition of at least two components (which are present as separate substrates) on one substrate, as a result of which composite materials are obtained. In addition, by means of the process, by generating gradients on the sputtered substrate, complete libraries of materials of differing composition can be generated.
The use of numerous different masks, which need to be positioned exactly to obtain reliable results, makes the process described complex to carry out.
It is an object of the present invention to provide a process for the combinatorial production of a library of materials, which process avoids the disadvantages of the known process.
We have found that this object is achieved by a process for the combinatorial production of a library of materials in the form of a two-dimensional matrix in the surface region of a planar substrate by sputtering, with the planar target used for the sputtering being arranged in parallel to the planar substrate and having surface regions of different chemical composition (e.g. a mosaic target).
In addition, the object is achieved according to the invention by a process for the combinatorial production of a library of materials in the surface region of a planar substrate by sputtering, with a ribbon-shaped substrate being shifted in the longitudinal direction and at least two targets of different chemical compositions which are used for the sputtering being arranged over the ribbon along the direction of shifting.
In the present invention the use of masks for generating the desired libraries is avoided, so that producing libraries is considerably simplified.
The fundamental idea of the mosaic target is that a materially inhomogeneous target for sputtering is used for the sputtering process, with a matrix of unknown composition being first produced by the sputtering process. Not until after successful testing for the desired physical or chemical property is the composition analyzed of the materials complying with the requirements. By coating the basic target with various other components, a gradient of the different components is produced on the sputtered matrix during the sputtering process. This gradient can be useful for producing alloys of metals and/or nonmetals, mixed oxides of metals and/or nonmetals or other classes of compounds of different compositions, provided that they are accessible by means of sputtering processes. By a suitable spatial arrangement of the components on the basic target, the sputtered matrix can be divided into sectors in which, in the manner of set theory, enrichment in each case of one of the components occurs, so that as great a range as possible of the potentially producible component mixtures can be generated.
Sputtering is the atomization of a solid surface by bombardment with high-energy ions such as O+ or Ar+ or neutral particles (FAB, fast atom beam bombardment). In sputtering, the kinetic energy of the primary particle, that is of the ions or neutral particles, is distributed by impact to the atoms of the solid (target). If in this process sufficient energy is transferred to a surface atom to overcome the surface binding energy, this can leave the solid as a free particle and be deposited on a substrate. In this manner, individual atoms, ions and clusters can be generated and deposited on substrates. The kinetic energy of the ions or neutral particles is generally from 0.1 to 20 keV. Suitable sputtering processes are known. Since the particles released have higher energies than thermally vaporized particles, they can be used for depositing thin layers on substrates, compared with what are termed PVD processes (Physical Vapor Deposition processes).
By selecting a target having surface regions of different composition, composition gradients of the material resulting on a substrate can be produced. Gradients of this type can also be achieved according to the invention by the material substrate being shifted spatially along a number of targets, the targets being excited in a phase-shifted manner.
Hitherto, sputtering processes have been used to generate compositions which are as homogeneous as possible, and not for generating gradients, cf. Ullmanns Encyclopedia of Industrial Chemistry, 6th Edition, 1998 Electronic Release, Wiley-VCH, Weinheim, Germany.
The term xe2x80x9clibrary of materialsxe2x80x9d means that a multiplicity of materials of different composition are generated on a substrate. Preferably, at least 10, particularly preferably at least 100, different materials are formed on the substrate.
The expression xe2x80x9cin the surface regionxe2x80x9d means that the materials are formed, for example, on a planar substrate, with the sputtered metals or nonmetals not penetrating into the substrate. This is the case, in particular, in the case of smooth ceramic, glass, plastic, metal, or carbon substrates. However, corresponding porous support materials can also be used, with the sputtered metals or nonmetals penetrating at least into the surface pores. In this case, according to the invention the material is formed in the topmost layer of the planar substrate, that is to say in the surface region.
The expression xe2x80x9cplanar substratexe2x80x9d means a substrate which extends considerably further in two directions in space than in the third direction in space. The planar substrate need not be flat, it can, for example, be a series of depressions or wells on or in a plate. For example, it can be a spot plate or a corresponding plate which has depressions at regular intervals. In particular, the porous support material can also be present in the form of bodies of any shape, for example in the form of tubes which have been cut open and divided into two halves that can be rejoined for a subsequent catalytic test. Preference is given to porous support materials made of ceramics, metals or activated carbons. Examples of such supports are described in DE-A-198 05 719 as auxiliary supports.
The exact configuration of the planar substrate is not restricted. Preferably, the planar substrate is subdivided into individual defined places which are spatially delimited from one another.
The expression xe2x80x9cplanar targetxe2x80x9d denotes a target which extends considerably further in two directions in space than in the third direction in space. The planar target, like the planar substrate, need not necessarily be flat. It can be provided on the surface, at least in part, with planar metal pieces and/or nonmetal pieces of at least one metal or nonmetal different from the target. The pieces can be fixed, for example, by glueing, soldering or welding. The spatial extension can then be chosen during the sputtering. The planar target can be arranged, for example, horizontally and can be coated on the surface at least in part with planar metal pieces and/or nonmetal pieces of at least one metal or nonmetal which is different from the target. In this case the target is sputtered from above.
The planar target is arranged in parallel to the planar substrate. This ensures that on the planar substrate a matrix of different materials is formed during the sputtering, since regions of different material compositions are present on the target. Slight deviations from parallelity of, for example, xc2x15xc2x0, preferably xc2x12xc2x0, can be tolerated in this case.
The target has surface regions of differing composition. In this case, at at least two different spatial positions of the target, different surface compositions are present.